A nitride semiconductor laser device has characteristics such as excellence in luminous efficiency, fast operability, and light focusing characteristic, and therefore is expected as a short-wavelength light source for reading and writing of information with respect to high-density optical recording media. Also, the nitride semiconductor laser device itself is capable of emitting visible light and, further, of converting short-wavelength light emitted from the nitride semiconductor laser device to visible light with the use of wavelength conversion means, and therefore is expected to be used as a visible light source such as a light and a back light.
In order to meet these expectations, it is essential to develop a nitride semiconductor laser device that has a high luminous output and is driven stably for a long period of time. However, conventional nitride semiconductor laser devices have insufficient durability because of the problem of poor adhesivity between the electrodes and the semiconductor, which causes the electrode to easily peel off. Thus, the abilities of the nitride semiconductor laser devices are not utilized effectively.
As a technique to overcome the problem, for example, techniques in patent documents 1 and 2 are proposed.
Patent document 1: Japanese Patent Application Publication No. 11-54843.
Patent document 2: Japanese Patent Application Publication No. 11-340569.
Patent document 1 discloses a technique to provide, as a p-side electrode, an Ni layer, a Ti layer, and an Au layer on a p-type nitride semiconductor. The Ni layer is a layer for obtaining an ohmic contact by coming into contact with the p-type nitride semiconductor, the Au layer is a layer as a bonding metal, and the Ti layer is a layer for preventing the p-side electrode from peeling off by intervening between the foregoing layers to enhance adhesivity.
With this technique, the problem of the electrode peeling off can be solved.
Patent document 2 discloses a technique to form on a p-type nitride semiconductor an electrode of a two-layer structure having a first layer and a second layer. Specifically, as the first layer, Ni, Pd, or Pt, which excel in ohmic characteristic, is used at a portion that is in contact with the p-type nitride semiconductor. As the second layer, a metal with high adhesivity (e.g., Cr, Al, and Ti) against an insulation layer that is formed as a buried layer on the semiconductor surface of the semiconductor laser is used. With this technique, the problem of the p-electrode peeling off can be solved.